Organometallic precursor processing has been used in recent years to prepare advanced materials such as aluminum nitride, aluminum oxynitride, titanium nitride, silicon carbide, silicon nitride, and boron nitride. This method has several advantages over classical techniques, e.g., relatively low temperature processing requirements, ease of control for maintaining high purity, and formability of the ultimately produced advanced materials into fibers, coatings, films, etc. Generally, the organometallic precursors are transformed into the corresponding advanced materials by a pyrolytic process. Aluminum oxynitride is a particularly useful advanced material having several desirable properties such as, for example, a high melting point, high hardness, excellent strength, high termal conductivity, optical clarity, and nonreactivity with a variety of other materials. These properties make aluminum oxynitride particularly suited for the preparation of electronic substrates, optical windows, vehicle armor, radar and infrared domes, crucibles, cutting tools, abrasive grit, etc.
The conventional method for preparing aluminum oxynitride involves the high temperature reaction of aluminum nitride and aluminum oxide. U.S. Pat. Nos. 4,241,000 to McCauley et al. and 4,720,362 to Gentilman et al. disclose admixing finely ground aluminum oxide and aluminum nitride, and ball milling the mixture in the presence of an alcohol. The resultant mixture is then dried, formed, and heated to a temperature in the range from 1,600.degree. C. to 1,800.degree. C., to form aluminum oxynitride.
U.S. Pat. No. 4,855,264 to Mathers et al. discloses an alternative method for making aluminum oxynitride, wherein alumina and carbon are heated in a nitrogen atmosphere to prepare aluminum nitride, which further reacts with the alumina at a temperature from 1,600.degree. C. to 1,900.degree. C. to form aluminum oxynitride.
U.S. Pat. No. 4,950,558 to Sarin discloses yet another method for preparing a coating of aluminum oxynitride by a chemical vapor deposition process. Aluminum chloride, ammonia, and carbon dioxide are reacted at a temperature from 900.degree. C. to 1,500.degree. C. to form the aluminum oxynitride.
In light of the prior art, there is recognized a need for developing a process to prepare aluminum oxynitride at a lower temperature.
In Doklady Akademii Nauk USSR, 114, 1033 (1957) and Chemical Abstracts, 52, 2742 (1958), a process is disclosed for reacting a hexaalkyldisiloxane and an aluminum halide, with the removal of trialkylhalosilane, to prepare a trialkylsiloxydihaloalane. The article does not, however, suggest that the trialkylsiloxydihaloalane would be useful for preparing aluminum oxynitride by a pyrolytic process.
It would be desirable to prepare aluminum oxynitride by a simple pyrolysis process which is carried out at a temperature lower than the reaction temperatures disclosed in the prior art.